Gas treatment towers typically are used to effect contact between a gas or gases which are to be subjected to treatment with a liquid or slurry which reacts with the gas or a component of the gas. The gas or gases are made to flow in a first direction in the tower while the liquid or slurry reactant flows in the opposed or counter-current direction. In a typical example a sulfur-containing flue gas may be subjected in such a tower to flue gas desulfurization (“FGD”) by being contacted with calcium carbonate slurry. However the present invention is not limited to use with any specific type of gas treatment tower; thus it can as well be used in various gas-liquid towers, including distillation columns and the like.
One or more perforated plates—so-called “sieve trays”—are commonly mounted in the tower flow path to serve as liquid-gas contact surfaces facilitating the liquid-gas reaction. (As used herein it will be understood that the term “liquid”, as in “gas-liquid contact”, is intended to encompass not only pure liquids, but as well flowable slurries such as the calcium carbonate slurry mentioned above.) The perforations in these sieve trays are commonly in the form of simple round holes of a diameter that is deemed appropriate for the intended materials being reacted. However while it is important to provide via the tray openings a large ratio between the open and closed space on the perforated surface, it is also important to preserve the integrity of the tray from a strength viewpoint. This is particularly important where higher gas velocities are used in the tower, as is often desired for maximum efficacy and efficiency.